Variable voltage transformer



April 27, 1931 L. E. SAUER VARIABLE VOLTAGE TRANSFORMER Filed Nov. 29, 1935 INVENTOR WITNESSES:

Patented Apr. 27, 1937 UNITED STATES PATENT OFFICE VARIABLE VOLTAGE TRANSFORMER Application November 29, 1935, Serial No. 52,147

8 Claims. (Cl. 171-119) This invention relates to transformers and particularly to transformers for delivering a variable voltage to testing instruments.

An object of this invention is to provide a transformer that shall be capable of delivering a voltage that may be varied through a wide range.

Another object of this invention is to provide a transformer suitable for testing instruments whereby the terminal voltage may be closely regulated over its variable range.

Other objects of this invention will in part be obvious and in part appear hereinafter.

This invention accordingly is disclosed in the embodiment thereof shown in the accompanying drawing and comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the system hereinafter set forth and in the scope of the application which will be indicated in the claims.

For a fuller understanding of the nature and objects of this invention, reference may be had to the following detailed description taken in conjunction with the accompanying drawing, in which Figure 1 is a diagrammatic view partly in section of the transformer and circuits embodied in this invention, Fig. 2 is an enlarged and elaborated view taken along the line II-II of Fig. 1 showing the position of the auxiliary windings embodied in this invention, and

Fig. 3 is an enlarged view taken along the line III-III of Fig. 1 showing the position of the auxiliary windings on the legs of the corememher as embodied in this invention.

Referring to the drawing and particularly Fig. 1, the transformer of this invention comprises the core i0 which is provided with legs ii, i2 and I3. A primary winding l4 and a secondary winding I! are disposed on legs II and I2, respec tively, of the core.

In order to control the flux traversing the legs i 2 and I3 of the transformer when the primary winding i4 is energized from a source oi power (not shown), auxiliary or control windings or wires I6 and I! are provided on the secondary leg I! and the shunt leg l3, respectively. The auxiliary windings l6 and i! comprise a plurality of coils l3, I3, 20, ii, 22 and 23 and 24, 25, 26, 21, Hand 29, respectively, so positioned with respect to the laminations of the legs of the core member that upon being short circuited as hereinafter described each of the windings will encircle a diflerent portion of its respective core leg.

The position of the coils of the auxiliary windlength and when assembled in a predetermined manner, ducts 32 will be formed along the top of the core legs. The ducts 32-are of a size suilicient for receiving a turn of one of the coils l3 through 23 or 24 through 230i the auxiliary windings l3 and i1, respectively. The ducts 32 may be spaced across the top of the core legs l2 and I3 as desired. The windings of the auxiliary windings are placed ih-the ducts 32 when the core is assembled.

A step switch 33 having taps I through 8 is provided for short circuiting the diflerent coils of the auxiliary windings i6 and I! in a predetermined manner. As shown in Fig. 2, the auxiliary winding l6 encircling the entire core leg i 2 is directly connected to switch 33 by conductor 34 and to tap i of the switch by conductor 35. The coils i8 through 23 on the core leg I2 are connected directly to one of the coils 24 through 29 by conductors 36, 31, 38, 39, 40 and 4i, respectively. The coils 24 through 29 are connected to taps i, 6, 5,4, 3 and 2 byconductors 42, 43, 44, 46, 46 and 41, respectively. Auxiliary winding i7 positioned about core leg I3 is connected by conductor 34 to the switch 33 and by conductor 48 to tap 8 of the switch.

In operation, when the primary winding i4 is energized and switch 33 is contacting tap l, the entire auxiliary winding l6 encircling the core leg i 2 is short circuited and of so low an impedance as to preclude any flux traversing the leg i2 about which the secondary winding I5 is disposed. Since the winding 'l'l about the core leg i3 is open, the flux produced in the core in response to the energization of the primary winding will traverse leg i3 instead of leg i2 and the voltage across the terminals of the secondary winding IE will be zero.

As the switch 33 is moved to tap 2, the auxiliary winding 16 is opened and a circuit including winding 23 is closed and only a portion of the core leg i2 is encircled by the auxiliary winding. A corresponding change in the auxiliary winding about the core leg i3 is encountered since coil 29 is included in the circuit when the switch 33 contacts tap 2. As is evident from the drawing, the amount of the core legs I2 and i3 encircled by the auxiliary windings is in an inverse ratio and, as the reluctance of core leg l3 increases, the reluctance of leg I2 decreases. The flux traversing the legs I! and I I will vary inversely as the reluctance of legs i2 and.v ll changes. When the reluctance of the core leg l3 increases and that of leg I! decreases, the flux traversing leg I! is so increased that a voltage will be encountered at the terminals of the secondary winding.

As the switch 33 is moved over contacts 2 through I, respectively, inverse proportions of the core legs I2 and II are encircled by the diil'erent coils of the auxiliary windings disposed on the respective legs and short circuited in a predetermined'manner. With the switch 33 contacting tap I, the reluctance of leg I3 is so great and that of leg I! so small that practically all of the flux resulting from energization of the primary winding I will link leg II. The voltage recorded at the terminals of the secondary windingunder these conditions is thus almost a maximum voltage for the transformer.

When the switch 33 contacts tap 3, a circuit is closed through conductor 3|, auxiliary winding I! about leg l3 and through conductor 43 to tap 8. With the switch in this position, the entire auxiliary winding il about the leg I! is short circuited whereas all of the auxiliary coils on the leg I! are open and all the flux traversing the core, links leg I2 upon whichthe secondary winding is disposed. Under these conditions maximum voltage is delivered at the terminals of the secondary winding of the transformer.

From the above description, it will be evident that as many voltage steps as is desired may be obtained by varying and spacing the number of coils disposed on the secondary and shunt legs of the core and so short circuiting'them to encircle'inverse portions of the legs to inversely control the flux traversing the respective legs.

It is, of course, evident that the coils of the throughout the length of the core legs although for ease of construction, it is desirable to place the coils in the Joint between the legs and the yoke of the core, as illustrated.

With this invention, it is possible to easily and economically construct a variable voltage transformer suitable for testing instruments without the necessity of providing a complicated control mechanism. The losses encountered-in the control windings of this invention are negligible.

Although this invention has been described with reference to a particular embodiment thereof, it is, of course, to be understood that other modifications thereof are possible. This invention is, therefore, not to be restricted except as is necessitated by the prior art and the scope of the appended claims.

I claim as my invention:

1. In a transformer, a core member comprising a plurality of legs, primary and secondary-windings associated with said core member, auxiliary windings on a plurality of the core legs, each of said auxiliary windings comprising a plurality of coils so disposed on its respective leg that each of the coilsencircies an amoimt of its leg that is different from the amount encircled by each of the other coils on the leg, means for connecting the, coils of the auxiliary windings in circuit, said means short circuiting certain of said plurality of coils to encircle inverse. amounts of the respective legs and to in versely vary the flux traversing. the respective legs.

2. he transformer, a core member comprising a plurality of legs, a primary coil disposed on one of the legs, an auxiliary winding and a secondary coil disposed on a second leg of the core member, an auxiliary winding disposed on another leg of the core member, each of the auxiliary windings comprising a plurality of coils so disposed that each of the coilsencircles a different amount of its respective leg from that encircled by each of the other coils of its respective winding, and means for inversely varying the amount of the respective legs of the core member encircled by the coils of the auxiliary windings for inversely varying the flux traversing the respective legs.

3. In a transformer, a core member comprising a plurality of legs, a primary coil disposed on one of the legs, an auxiliary winding and a secondary coil disposed on a second leg, an auxiliary winding disposed on a third leg, each of the auxiliary windings comprising a plurality of coils each of which is adapted to encircle a different amount of its respective leg from that encircled by each of the other coils of its respective auxiliary winding, means for connecting the coils of the auxiliary windings in circuit. said means being adapted to vary the connections between the auxiliary windings to inversely vary the amount of the respective legs encircled by the coils of the auxiliary windings and inversely vary the flux traversing the respective legs.

4. In a transformer, a core member comprising a plurality of legs, a primary coil disposed on one of the legs, an auxiliary winding and a secondary coil disposed on a second leg of the core member, an auxiliary winding disposed on another leg of the core member, each of the auxiliary windings comprising a plurality of coils. means for connecting the coils of the auxiliary windings in circuit to short circuit certain of the plurality of coils of each of the auxiliary'windings to encircle inverse amounts of the respective legs and to inversely vary the flux traversing the respective legs.

5. In a transformer, a core member comprising a plurality of legs, a prlmarycoil disposed on one of the legs, an auxiliary winding and a secondary coil disposed on a second leg of the coremember. an auxiliary winding disposed on another leg of the core member, each of the auxiliary windings comprising a plurality of coils disposed in spaced I relation through the respective legs, means for connecting the auxiliary windings in circuit, said means short circuiting certain of the spaced coils to encircle inverse amounts of the respective legs and to vary the flux traversing the respective legs.

6. In a transformer, a core member comprising a plurality of legs, a primary coil disposed on one of the legs, an auxiliary winding and a secondary coil disposed on a second leg of the core member, an auxiliary winding disposed on another leg of the core member, each of the aux-. iliary windings comprising a plurality of coils disposed in spaced relation through its respective leg, means for connecting the auxiliary windings in circuit in a predetermined manner, said means short circuiting certain oi' the spaced coils to encircle inverse amounts of the respective legs to inversely vary the flux traversing the respective legs.

7. In a transformer, a core member comprising a plurality of legs, a primary coil disposed on one of the legs, an auxiliary winding and a secondary coil disposed on a second leg of the core member, an auxiliary winding disposed on another leg of the core member, each of the auxiliary windings comprising a plurality of coils disposed in spaced relation through its respective leg, and means for connecting certain of the coils of the auxiliary windings in circuit in a predetermined manner, said means adapted to short circuit the spaced coils connected in the circuit whereby inverse amounts oi the respective legs are encircled to inversely vary the flux traversing the respective legs.

8. In a transformer, a core member comprising a plurality of legs, a primary coil disposed on one of the legs, an auxiliary winding and a secondary coil disposed on a second leg of the core member, an auxiliary winding disposed on a third leg 01' the core member, each of the auxiliary windings comprising a plurality of coils each of which is adapted to encircle adifierent amount of its respective leg from that encircled by each of the other coils of its respective winding, and

means for connecting certain of the coils oi the auxiliary windings in circuit in a predetermined manner, said means adapted to short circuit the coils connected in the circuit whereby the amount of the respective legs encircled by the short circuited coils may vary from all to none of said second leg as the amount of said third leg en circled varies from none to all, thereby inversely varying the flux traversing the respective legs. LOUIS E. BAUER. 

